The present invention relates to a synthetic fiber rope, preferably of aromatic polyamide, with load-bearing strands of bonded synthetic fibers, preferably being laid in an outermost layer of strands on a rope core made up of load-bearing synthetic fiber strands laid together in layers, and a coating surrounding at least the load-bearing synthetic fiber strands of the outermost layer of strands.
In conveying technology, for example such as on elevators, in crane construction, and in open-pit mining, moving ropes are an important element of machinery and subject to heavy use. An especially complex aspect is the loading of driven ropes, over pulley deflected ropes or ropes wound on drums, for example as they are used in elevator construction and for suspended cable cars. In these instances the lengths of rope needed are large, and considerations of energy lead to the demand for smallest possible masses. High-tensile synthetic fiber ropes, for example of aromatic polyamides or aramides with highly oriented molecule, chains, fulfil these requirements better than conventional steel ropes. However, materials such as aramides are particularly sensitive to ultraviolet (UV) light, and environments having an oxidizing or reducing effect, which cause the breaking stress and work capacity to be diminished. For this reason, aramide ropes usually are covered with a sheath or braid of material that is stable to light.
For example, from the European patent document 0 672 781 A1, it is known to use such sheathed synthetic fiber ropes for the suspension elements of elevator installations, so as to connect the car frame of a car which is guided in an elevator hoistway to a counterweight. To raise and lower the car and the counterweight, the rope runs over a traction sheave that is driven by a drive motor. The drive torque is transferred by friction to the section of rope that at any moment is lying in the angle of wrap.
In this example, instead of there being a sheath surrounding the entire covering layer of strands, each individual strand of this layer is given a seamless extruded sheath of synthetic material, preferably polyurethane or polyamide, all of these together serving as a protection against abrasion of the rope, and ensuring the desired coefficient of friction on the traction sheave.
In this case, the adhesive forces between the sheaths of synthetic material and the outermost layer of synthetic fiber strands are achieved by the sheath of synthetic material being extruded on under pressure, so that all interstices between the strands are filled, and a form-fit with a large area of adhesion is created. Under certain conditions, however, the transverse forces that arise when the rope is loaded can cause displacement or piling-up of the synthetic sheath. Such changes in the rope are undesirable, as they could lead to failure of the rope. However, using the extrusion process to apply to the strands the sheath needed to create the necessary adhesive forces between the strands and the sheath is expensive.
An objective of the present invention is to reduce the cost of producing a synthetic fiber rope, while ensuring an unchanged high level of functionality.
Extensive tests by the applicant have shown that instead of an extruded protective sheath as hitherto used, lasting assurance of reliable protection against UV, as well as adequate resistance of the rope to abrasion, can be achieved by only coating the synthetic fiber strands in the outermost layer of strands with liquid containing UV stabilizers arid other additives as protection against abrasion and environmental influences damaging to the rope.
The advantages resulting from the present invention consist of a lasting bond of the coating to the synthetic fiber strands of the outermost layer of strands, because the material of the coating and of the matrix binding the synthetic fibers of the strands is the same. By simply admixing appropriate additives the functionality can be easily extended to the entire lifetime of fiber ropes. The coating according to the present invention does not form pile-ups, nor can it be displaced on the synthetic fiber strands. Manufacture of the coating takes place to a large extent without additional expense for tools and equipment, and is simple and inexpensive. Taking large-series manufactured conventional synthetic fiber strands as the starting point, the synthetic fiber strands for the outermost layer of fiber strands have only to be drawn through an impregnating bath, which is present in any case, to form the coating according to the invention. The thickness of the coating can be adjusted via the time spent by the synthetic fiber strands in the impregnating bath. Furthermore, the coating process can be repeated an unlimited number of times.
A particularly abrasion-resistant embodiment of the coating is achieved by adding short fibers, consisting for example of aramide, to the impregnating bath.